The evolutionarily conserved Hedgehog (Hh) signaling pathway plays a crucial role in many developmental and disease processes. Hh, secreted protein ligand, initiates a signaling cascade in the receiving cell through binding to its membrane receptor Patched. Ptchd3 has been recently identified as a male germ cell-specific gene in our laboratory and is conserved among many organisms, including human, mouse and zebrafish. It contains a conserved Patched domain and is predicted to have Hh receptor activity. In vertebrates, there are three members of the Hh family, Sonic hedgehog (Shh), Indian hedgehog (Ihh) and Desert hedgehog (Dhh). Dhh is the only Hh family member that is expressed in testis, specifically, in Sertoli cells. Previous studies have demonstrated that Dhh is essential for spermatogenesis---a highly ordered, precisely orchestrated developmental process in which male germ cells proliferate and differentiate to produce sperm. The molecular mechanism of Dhh function during spermatogenesis, however, is unknown. In this application, we propose to test the hypothesis that Ptchd3 is a novel Dhh receptor on male germ cells and mediates Dhh effect on spermatogenesis. Two specific aims will be carried out to test our hypothesis. In Aim 1, we will investigate if Ptchd3 is a component of Dhh signaling in spermatogenic cells by a broad spectrum of assays, including biochemical, genetic, pharmacological, molecular and cellular approaches. In Aim 2, we will determine if Ptchd3 is required for spermatogenesis by using Ptchd3 null mutant mice. These studies constitute one step toward attainment of our long-term research goal- --understanding the molecular and cellular mechanisms of mammalian reproduction. Results from these studies will advance our knowledge about the regulation of spermatogenesis, may provide insight into unexplained (or idiopathic) infertility in men, and may lead to new strategies for male contraception. PUBLIC HEALTH RELEVANCE: Results from these studies will advance our knowledge about the regulation of spermatogenesis, may provide insight into unexplained (or idiopathic) infertility in men, and may lead to new strategies for male contraception.